This invention relates to an improved extrusion die for producing a multicomponent continuous polymer film, especially a striped thermoplastic polymer film useful in making yarns.
For a number of years, multicomponent polymer films have been extruded for making yarns. In particular, yarns suitable for heavy duty uses such as indoor-outdoor carpets have been produced from such multicomponent films. It is known to fibrillate and slit thermoplastic films into narrow webs which can then be twisted into yarns and twines. By using a multicolored film or striped film, different color effects can be obtained when the fibrillated web is twisted, to afford esthetically pleasing color combinations.
A multicomponent extrusion die which can be used to extrude such a film is described in U.S. Pat. No. 3,807,918. Although generally this prior art die performs satisfactorily, it has certain disadvantages. The prior art die employs a flow splitting insert which comprises a bar with an array of outlets, supplied with molten polymer from a common conduit. The outlets, in embodiments in the prior art, are cylindrical holes drilled in the bar. Each outlet extrudes a stream of polymer which is intended to form a stripe of a longitudinal width greater than the longitudinal width of the outlet. The prior art die has internal dead areas in which the viscous polymer can stagnate. The stagnation can lead to overheating and degrading of the stagnated polymer. Moreover, the prior art die may produce polymer streams with non-uniform velocity, since the polymer stream must spread out after exiting the outlet. In addition, the outlet holes of the prior art die are difficult to clean.